This invention relates to the structure of the walls of a vacuum processing chamber and a method for producing vacuum processing chambers using extrusion technology to provide options and unexpected process improvements in processing semiconductor wafers.
In vacuum processing in general, and in processing of substrates on which electronic elements are being formed in particular, the speed with which vacuum pressure is achieved in a vacuum chamber is a critical path step in achieving specified vacuum process conditions so that substrates can be cycled and processed. Similarly, once stable substrate processing conditions are achieved, maintaining the integrity of the low pressure process requires that the process environment remain stable by minimizing pressure transients both short and long term which may cause or contribute to anomalies in process conditions.
The current state of the art is such that short fat substrate vacuum processing chambers are machined from a solid block of the base material. As a result, as much as 80% of the material is cut away before the final chamber configuration is arrived at. Similarly in cluster arrangements of processing chambers, the cluster tool housing is carved (machined) from a large block of the base material, again, much of it is wasted as it is cut away. The base material, usually a cast piece is specified to include a high degree of quality (material integrity) to assure that there are no openings through which gasses may leak into the chambers.
When tall narrow vacuum chambers are needed, the technique of machining material away from a block of base material is abandoned in favor of using large thick plates. Such plates are bent 90xc2x0 to form an L-shaped cross section. An example of L-shaped cross section plates is shown in FIG. 1 (e.g., 22). Four of these L-shaped cross sections are welded together at their edges using butt welding techniques to form a tube which acts as the wall of the processing chamber. An example of the construction of this type of prior art arrangement is shown in FIG. 1. A set of four corner panels 22, 24, 26, and 28, having been bent into L-shaped pieces are complimented by a top plate 32 and a bottom plate 34. The location of a future substrate access opening is shown by dashed lines 30. The whole configuration of elements defines a process chamber assembly 20, which in this case is a relatively tall and thin load lock module as would be used associated with a cluster tool.
Once fixed elements of the process chamber assembly are joined by welding the configuration as seen in FIG. 2 is formed. The four corner panels 22, 24, 26, 28 having been welded together by four butt weld type joints whose weld region and heat affected zone are depicted by weld regions 52, 54, 56, and 58. Welding is done inside and out. Since the only performance criteria for the welds is pressure sealing, grinding and multipass welding is not uniformly performed, as is done in welds where the highest degree of quality assurance is required by specification. The bottom plate 34 is welded to the bottom of the tube formed by the welded plates. The weld region and heat affected zone of the bottom weld is represented by the lower weld area (heat affected zone) 60. Again the welding is done both inside and out, the inside weld being difficult to perform as it is being done at the bottom end extreme corner of a narrow closed end tube. Both the sidewall and bottom plate welds are minimally inspected and often contain inclusion, voids, and porosity.
Similarly the corners of the sidewall plates where they were bent contain, surface defects which are created or accentuated by the bending of the thick plate (for examplexe2x80x94xc2xe inches (19.05 mm) thick).
As a result of the side and bottom plates being welded their final dimensions are uncertain, for example an O-ring groove 44 (shown in FIG. 3) in the end surface of the tube assembly, is intended to be centered in the end surface, with a particular configuration. Because the locations (dimensions) of the inside and outside surfaces vary slightly depending on how the welding was completed, before machining a rectangularly configured O-ring groove in the end surface of the tube, a machinist or machine tool must go through measuring steps to find a datum line between the inside and outside surfaces and then calculate where the machining should take place so that the O-ring groove when completed does not approach either an inner or an outer surface too closely.
An end view of the processing chamber of FIG. 2 is shown in FIG. 3. The locations of heat affected, weld zones are shown on each side (e.g., 42). The O-ring groove 44 is cut in the end surface to mate with the removable (top) cover plate.
A parameter specified in the material specification for a finished product is surface finish. Once all welding and machining is complete, a specified surface finish must be achieved on the surfaces of the plates both inside and out. Often the treatment of the surfaces to achieve a specified surface finish is a hand operation which is time consuming and variable. Inspection of such finishes is also subject to high rate of rejection for refinishing. It would be preferred to reduce the variability, improve uniformity, and reduce the time associated with achieving an acceptable surface finish.
Conventional vacuum chamber vacuum standards, find both machined and welded vacuum chamber structures acceptable when they are deemed tight, in that a vacuum pressure of 10xe2x88x929 torr can be reached quickly and vacuum pressures of 10xe2x88x925 to 10xe2x88x928 torr can be maintained during processing. Improvements in vacuum performance are desired as a typical pumpdown time for a system is 20% (at the initial stage and further pump down required every time a wafer is being loaded and unloaded). A reduction in the pump down time can significantly affect product throughput.
A configuration and method according to the invention provides an unexpected improvement in vacuum chamber and vacuum processing within vacuum chambers in that the time to achieve a vacuum level of 10xe2x88x929 torr is significantly reduced (approximately 15%) from that when using welded structures. Further, the use of an extrusion die provides a consistency and uniformity among all extrusions being drawn from the same die. Therefore, the time steps needed to perform datum measurements, necessary to effectively machine welded structures, are not necessary when extruded structures are used. Further, use of an extruded structure eliminates the volumetric porosity in the wall material, reduces surface cracking, provides a consistent surface finish, and eliminates undesirable inclusions that readily appear when large plates are bent and then welded. Because of the high degree of material integrity in the wall of the chamber and the elimination of side wall welds and complications associated with machining through such welds, both the bottom and top edges of the extruded tube can be machined for O-ring grooves to receive top and bottom sealing plates which can be bolted to the top and bottom of the extruded tube. Such bolting eliminates the need for special treatment and/or quality control when using a welded joint and also reduces the complications associated with constructing and using a pressure vessel having an end which has been welded shut. Those complications include the requirement that a portion of the well be done deep inside a tube at its end. In the prior art structure, is hard to check the integrity of such a weld. Cleaning of a vacuum chamber constructed with a closed end (as in the prior art) requires careful attention to cleaning of the extreme bottom end and the corner between the end cap and the side wall to be sure that all deleterious substances are removed. In contrast, a structure according to present invention allows the end caps to be removed to access the inside of the side walls easily from both ends which thereby eliminates corners once the top and bottom plates are removed. In this configuration the side walls can be cleaned directly and the top and bottom plates can be cleaned directly as well.
In an extruded configuration according to the present invention, it is possible to extrude a pressure vessel side wall while including voids or tubes in the side wall separated from the pressure vessel space. In such an arrangement, cooling or heating liquid can be circulated through the separate tubes to directly heat or cool the side of the pressure vessel. Such an arrangement/configuration provides greatly increased efficiency in terms of the production of a heated or cooled pressure vessel by eliminating the step of having to attach by welding, brazing or other methods, a set of cooling type coils or pipes carrying a thermal transfer liquid to the outside of a pressure vessel. Secondly, the integration of the cooling channels enhances the transfer of thermal energy between the liquid flowing through the cooling/hearing channels and the material of the side well, as compared to the small weld or brazing area that is utilized when external tubing or piping is welded or brazed to the outside of a pressure vessel. Any imperfect connection between such tubing and a pressure vessel would cause differential thermal expansion which may create gaps that further reduce the thermal conductivity between the fluid flowing and the cooling channels in the side wall of the chamber.
In a preferred configuration, linear tubing passages are configured within the wall of the chamber. The ends of the heat transfer tubes in the walls of the chamber are connected by a series of connecting conduits between individual passages of the series of preferably tubular passages. Or, the ends of conduits in the wall can be undercut to provide a passage between adjacent tubes at the top and bottom of the extruded sidewall ends so that a flat plate covering the tube and passages will seal the fluid passage between adjacent individual passages.
A 15% improvement in pumpdown time translates into a 3% overall improvement in substrate (wafer) throughput. A leak rate improvement of three to five times can translate into a 3 to 5% faster throughput cycle. Since a 0.25% throughput improvement is considered xe2x80x9csignificantxe2x80x9d in the substrate processing industry, a 3 to 5% improvement is not only significant, but substantial.
A method according to the invention includes the steps of extruding a tube to be used as pressure vessel; machining its ends surfaces to receive O-rings and machining its side surfaces to accommodate transfer mechanisms and doors as needed for processing operations.